Method of manufacturing a multitrack magnetic head employing double helix structure

ABSTRACT

A multitrack magnetic head is made from an electrically conductive first helix formed on an iron wire that is, in turn, wound to form a second helix. By cutting or lapping a longitudinal flat along one side of the second helix, the first helix is severed into respective discrete coil-wound gapped cores.

This is a division of application Ser. No. 083,036 filed Oct. 9, 1979, now U.S. Pat. No. 4,316,227.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to multitrack magnetic heads and to methods and parts for forming such heads.

2. Description of the Prior Art

In the art of magnetic recording, there is a trend toward the use of multitrack magnetic heads having large numbers of cores per unit width across the head surface that interacts with the recording medium. One explanation for this trend may be found in the fact that a plurality of head cores can record a specific amount of data at an information writing speed which is only about ##EQU1## of the information writing speed which would be required when writing with only one core. For example, for a playback gap length of, say, 100μ" (μ"=microinch), a bandwidth of 2 mHz would necessitate a single core writing speed of 200 inches per second (ips) if use of the recording medium is to be optimized. By contrast (still using playback gap lengths of 100μ"), that same bandwidth of 2 mHz can be written by a 500-track record heat at a relative head-to-medium speed of only 0.4 ips ##EQU2## Such recording of a large bandwidth in a large number of tracks at low writing speed suggests, among other things, the linear tape recording of video information. Linear tape recording of video information, as opposed to the recording techniques employed in helical scan and quadruplex video recorders, implies a simplification of hardware: not only does a lessened information writing speed relax the mechanical demands of the recording operation, but head switching, rotary head drums, and various electronics are obviated, as well.

Perhaps the most common technique for forming a multitrack magnetic head is that which is shown generally in U.S. Pat. No. 4,084,199. Such a technique is characterized by the respective winding of coils on discrete cores, and the positioning of the coil-supporting cores in thin slots in a head block. Because of the tedium inherent in the winding of coils on tiny cores, and because of the brittleness associated with the slotting of the head block, a head made according to the teaching of U.S. Pat. No. 4,084,199 is generally limited to about 30 tracks per widthwise inch of the recording medium. In an attempt to increase the number and density of discrete cores in a multitrack magnetic head, various head manufacturing techniques employing photolithography have been suggested, thereby to avoid the need for discrete coil winding and to avoid the requirement for sawing thin slots in a head block. U.S. Pat. Nos. 3,893,189 and 3,983,622 are representative of such techniques.

While photolithography and similar techniques hold promise for future developments in the art of multitrack magnetic heads, it must, however, be realized that such techniques have limited versatility when it comes to providing multitrack magnetic heads of varying design. It would, for example, be desirable to have a multitrack magnetic head which is such that, when made from a basic core material, variations in the resultant head design can be provided relatively easily, and without ado. In other words, were it desired, for example, to provide a multitrack magnetic head of N cores with M turns per core, or a multitrack magnetic head of X cores with Y turns per core, such could be provided handily from the same basic core material.

U.S. Pat. No. 4,314,298 discloses an invention in which a double helix core-and-coil structure is provided, the preselectable length of such double helix core-and-coil structure being determinant of the number of cores which are to be employed in a head under construction. One helix of the double helix core-and-coil structure constitutes an electrically conductive coil wrapped on a magnetic wire; and which magnetic wire is, itself, helically wound to form the second helix of the double helix core-and-coil structure. By longitudinally cutting through one side of the double helix core-and-coil structure, a succession of gapped cores is provided; and by judiciously contacting the electrically conductive helix, supported by the magnetic helix, at a predetermined arc of the magnetic helix, the number of turns of the coils in question may be selected. (The term "gap", as used herein, does not necessarily mean "transducer gap". Rather, "gap" shall be interpreted to mean any break in an otherwise continuous form, and which break may or may not constitute a "transducer gap".)

As taught in U.S. Pat. No. 4,314,298, the double helix core-and-coil structure is formed on a removable mandrel; and which mandrel is removed during head manufacture to permit the inherent helical twists in the gapped cores to be cancelled by relatively shifting the core parts which define the respective core gaps. Such a procedure, according to the present invention, may be eliminated, thereby to produce a multitrack head which is not only easier to make, but which is structurally better . . . and which, when worn out, will provide an expensive-to-build part for the "reconstruction" of a new head.

SUMMARY OF THE INVENTION

In accordance with the present invention, the double helix core-and-coil structure which is formed on a mandrel is processed to provide the mandrel-supported structure with a flat. In so providing the flat, the double helix core-and-coil structure is converted into a succession of individual coil-wound cores, each of which has a helical twist therein. Rather than remove such twists, as taught in U.S. Pat. No. 4,314,298, the present invention teaches the use of a cooperative pole tip piece comprising a plurality of pole tip pairs, such pole tip pairs defining a gap line, and being skewed relative to the gap line in proportion to the core twists, thereby to compensate for such core twists. Because the double helix core-and-coil structure remains on its mandrel during and afer head manufacture, a head made as taught herein is inherently stronger than one made by the teaching of U.S. Pat. No. 4,314,298. And, it will be appreciated, when the pole tip piece of a head made as taught herein wears out, it may be removed, the flat of the double helix core-and-coil structure reprocessed, and a new pole tip piece installed. Since the coil-supporting cores constitute the most intricate and expensive part of a head, the prior art discarding of such cores is, by means of the present invention, avoided.

The invention will be described with reference to the figures, wherein:

FIG. 1 is a side view showing one helix of the double helix core-and-coil structure;

FIG. 2 is a side view showing the double helix core-and-coil structure;

FIGS. 3a, 3b and 3c are, respectively, plan, edge and side views of apparatus employed in the practice of the invention;

FIGS. 4a, 4b and 4c are, respectively, edge, side and bottom views depicting a flat formed in the double helix core-and-coil structure;

FIGS. 5 and 6 are perspective views showing parts of a head embodying the invention; and

FIGS. 7a and 7b are side and plan views useful in describing a multitrack magnetic head embodying the invention.

A multitrack magnetic head having 252 coil-wound cores per widthwise inch of the head, and which head embodies the invention, will now be described in terms of its method of manufacture:

Referring to FIG. 1, a very fine insulation-covered copper wire 10 (0.0009 inch in diameter) is helically wound into a coil along and about the length of an iron wire 12 (0.002 inch in diameter). Then, as depicted in FIG. 2, the coil-supporting iron wire 12 is, itself, helically wound on a mandrel 14, thereby forming the basic double helix core-and-coil structure. (It will be appreciated that the double helix core-and-coil structure may be provided, and stocked, in large spools and/or skeins thereof, whereby multitrack heads of various numbers of cores may be provided depending upon the length of the double helix core-and-coil structure which is employed.) The mandrel 14, which in this case has a circular cross-section of 0.022 inch in diameter, is then laid along the length of a groove 16 in a nonmagnetic jig 18. See FIGS. 3a, 3b and 3c. After the double helix core-and-coil structure is bonded in place in the groove 16 by epoxy 19, parts of the jig 18 are cut or lapped away, thereby exposing rows of electrical contact points 20 to which electrical leads may be bonded. See FIGS. 4a, 4b and 4c. The double helix core-and-coil structure is then lapped to provide a flat 22 on the double helix core-and-coil structure, the flat 22 effectively converting the double helix core-and-coil structure into a row of helically twisted, individual, coil-wound cores 21. (It will be appreciated, as was described in U.S. Pat. No. 4,314,298, that different numbers of turns on the individual cores may be provided, simply, by proper angling of the cut or lap lines c--c). A channel 24 is then cut into the mandrel 14 to accommodate a common bias lead 26 (FIG. 5) for the cores 21, the lead 26 being bonded in place by suitable means 28. Leads 30 from ribbon cables 32 are then ball-bond soldered respectively to the electrical contact points 20; and, although it will be usual to bring leads 30 to all of the contact points 20, it will, of course, be possible to vary the number and density of the active cores 21 of the head under construction by selectively bonding leads to different ones of the contact points 20. (For example, if it is desired to provide a 126 track head, instead of a 252 track head, every other lead of the ribbon cables 32 is simply left opened.)

The ribbon cables 32 are the embedded in epoxy 34 (FIG. 6), thereby forming an integral structure of `cores, coils and leads` . . . and which structure may be used over and over again with successive pole tip pieces.

In accordance with a principal aspect of this invention, a pole tip piece 36 (see FIGS. 7a and 7b) having individual magnetic pole tip pairs 38, 40, etc, which are skewed relative to high reluctance gap line 42 (by an amount corresponding to the helical twists left in the cores 21) is then bonded at 43 to the integral structure of FIG. 6 in such a way that pole pair mate with, and magnetically couple (as at 44) to, respective cores 21. This procedure obviates the need to untwist individual cores.

To replace a pole tip piece 36 which has worn out, the epoxy bond 43 of FIG. 7a is simply broken, the pole tip piece removed, and the flat 22 lapped clean to accommodate a new pole tip piece.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 

What is claimed is:
 1. The method of making a multitrack magnetic head comprising the steps of:(a) severing a length of magnetic material which has been wound on a mandrel into a succession of gapped cores by lapping or cutting a longitudinal flat into said mandrel; and (b) bonding a pole tip piece comprised of discrete pole tip pairs to said mandrel-supported cores in such a way that discrete pole tip pairs magnetically couple to respective cores on said mandrel.
 2. The method of claim 1 wherein said length of magnetic material is such that it, prior to being processed into a succession of gapped cores, is provided along its length with a substantially helical coil of electrically conductive wire.
 3. A method for use in forming a multitrack magnetic head comprising:(a) substantially helically winding electrical wire along a length of magnetic wire; (b) substantially helically winding the magnetic wire having the electrical wire thereon on an elongated mandrel; and (c) lapping along the length of said wire-supporting mandrel so as to form a flat on said mandrel and to sever the magnetic and electrical wire into a plurality of discrete coil-wound cores on said mandrel, said method further including the additional step of bonding a pole tip piece having a gap line to the flat of said mandrel, the pole tip piece having respective pole tip pairs which are skewed with respect to said gap line by an amount sufficient to permit coupling to respective cores on said mandrel. 